Iris rhizomes

I have 3 iris rhizomes which I received from a free news paper offer but the bed I'm planting them in has some plants and climbers in that I haven't cut down yet as they are still flowering. I was wondering if I could plant them in pots just for now and plant out next spring when the bed is prepared properly ? Which brings me to my next question - I have only seed compost at the moment . Could I use this or would I be better purchasing a new bag of compost ?

Jean-they would prefer a JI3 type of compost, but some of your garden soil/own compost, if any, should be fine as a temporary measure. Seems daft buying a new bag at this time of year. (Says she who justs need a very small bag of MP to quickly repot a bargain houseplant. Have JI3 but that'll be too good for it, plus I need most of it for repotting a patio clematis into a bigger pot.) J.